There are several prior inventions for portable sawmills.
U.S. Pat. No. 5,784,941 describes a portable sawmill in which the functions of adjusting a cut and making a cut are divided between two separate devices. The invention discloses a vertical chain saw, ideally operated in an upward direction. The patent also discloses a log restraint system comprising a setwork having a headstock and a lockable L-shaped log dog, joined by a clamp which is locked with a lever.
U.S. Pat. No. 5,243,892 discloses a portable sawmill with a frame base and an inverted U-shaped frame, supported by a carriage rolling along side tracks defined by the frame base. In use, the log is placed on the U-shaped frame and clamped with a tubular clamp held within a sleeve and locked in place using threaded blocks.
U.S. Pat. No. 4,640,170 discloses a portable saw mill with a frame that surrounds the log. The frame is dragged or slid along a frame supporting surface. The frame holds a chain saw at the two ends of its blade, in horizontal fashion, with chain saw support members. The invention uses sliding means for facilitating the movement of the frame over the log. The log is secured against rolling using a simple jig or similar means.
U.S. Pat. No. 4,275,632 describes a portable sawmill comprising a U-shaped support or carriage, holding a band saw. When in use, a log is placed between the two guide rails and is supported in place by appropriately distanced log supports.
U.S. Pat. No. 4,307,641 describes a portable sawmill comprising two skid rails, vertical support members, a pair of guide rails. The log is held in place by two externally threaded log screw pins with pointed ends.
U.S. Pat. No. 4,300,428 describes a portable sawmill having a frame, a guide member mounted above the frame, and a carriage. The chain saw is mounted above the log, and operates at about a 45 degree angle to the horizontal. The log is held in place with log dogs which are adapted for hooking the log and holding it in position.
U.S. Pat. No. 4,235,140 describes a saw mill. The logs are held in place with a standard log dog attached to the cross members on which the log is placed.
U.S. Pat. No. 3,965,788 describes a saw guide for use with a vertically operated portable chain saw. The saw guide apparatus is attached directly to the log.
U.S. Pat. No. 3,926,086 describes a portable saw mill that uses a complex pulley system to move the chain saw and supporting platform. When in use, a log is placed, and clamped, between the guide rails, using a set of circular discs eccentrically oriented on a rod.
U.S. Pat. No. 3,695,316 describes a portable timber milling jig that uses a carriage, holding a chain saw, axially surrounding a square guide rail. The chain saw is held at an approximately 45 degree angle and only uses one guide rail, and utilizes ball bearings on the carriage to move the carriage with respect to the guide rail. When in use, a log is placed under the guide rail, and fixed using clamping points driven into the center of the log, to which support clamps are fastened.
Canadian Patent No. 1,200,180 describes a portable saw mill comprising a frame with a guide rail and a carriage moveable along the guide rail. A band saw is supported by the carriage. The carriage is moveable along the guide rail along two sets of wheels, one engaged with the upper side of the guide rail and the other with the lower side. The log is held in place by its own weight, or by stops and a traditional locking dog.
U.S. Pat. No. 4,245,535 describes a portable sawmill with an elaborate hydraulic apparatus for cutting a log. The chain saw cuts in a vertical motion. The log is held in place using a log holding assembly having a toothed prod which grips the outer end of the log, and a cylinder which impales the inner end of the log with a ram, forcing the outer end against the prod.
U.S. Pat. No. 4,210,049 describes an “x” frame for holding a log, with a chain saw affixed to the frame in cantilever position for cutting logs crosswise. The log is held in the nook of the “x” frame.
Canadian patent application 2,541,734 describes a portable sawmill that is easily displaceable, easily assembled and disassembled into portable components, and which can use generic components as its saw and/or guide rails. The log is held in place using traditional log dogs.
Canadian patent application 2,687,623 describes a log support system (log rest) for a portable sawmill. The log rest features a ratcheting, adjustable clamp which allows a user to affix the log in place for sawing. To lower the log rest, a pawl is disengaged from the log, the log rest is manually lowered, and the pawl is re-engaged.
In all cases, the log rest is on the opposite side of the log from the log dog. Accordingly, when the sawmill bed is wide, two operators are required to adjust the log rest and log dog, or the operator must lean over the bed and log (which can inconvenient, if not dangerous), or the operator must walk around the log. Leaning over also strains the back. Walking around is time consuming. As the log rest and log dog must be lowered as the top of the log is removed by cuts, this task must be repeated multiple times.